1. Field of the Invention
The present invention relates to a three-dimensional display through which a three-dimensional vision can be observed, utilizing the parallax of the right and left eyes. The three-dimensional display is applied to the three-dimensional visualization of CAD, CAM and the like, and the three-dimensional visualization of Internet information as a terminal display of a computer for instance, as well as the three-dimensional visualization of computer games, three-dimensional display in the fields of medical care or art and so on.
2. Description of the Related Art
Influenced by the progress in information terminal which centers personal computers as a main tool, growth of the information network which is represented by the Internet, the amount of information handled by individuals is rapidly increasing. Particularly, concerning about image information, there has arisen loud calls for display equipment which can express more accurate and more real images, in accordance with the increase of information manageable for individuals due to the improvement on compression and transmission technology thereof. In order to respond to such a request, improvement to higher definition and the like has been made in various display devices such as LCD, EL panel, CRT and so on.
A latent demand is strong for the three-dimensional visualization to apply to an industrial use, a commercial use of such as a virtual mall and the like, and an amusement use of such as games and the like. However, for instance, when the liquid crystal optical shuttering method is used to materialize the demand, due to the limitation of the size of the optical shutter, the spectacles must have a shutter function, therefore it is not easy to say that the method is getting sufficient popularity because of its sense of incompatibility.
It has been long known that a pseudostereoscopic view can be obtained by simultaneously watching two different images with each right and left eye respectively. As a method to obtain three-dimensional images of two photographs and the like with the naked eyes, a parallel method and an intersection method have been known. When using these methods, however, training of viewers for the method is usually required. In addition, the size of the two images, and the distance of the two images placed can not be freely changed.
On the other hand, there is another method called the anaglyph method. An image for the right eye and an image for the left eye are drawn in a write-over manner with different colors. That is, the viewer puts on a pair of colored glasses which passes different colors through right and left glasses (for instance, red and blue). Separately watching the breakdown images with a right eye and a left eye can give the image a three-dimensional look. In this method, there is no limitation for the size of image, but it has a disadvantage that the coloring of the image may be spoiled because the method uses 2 colored filters.
Recently, many methods which can obtain a three-dimensional image have been proposed, utilizing a liquid crystal cell as an optical shutter. A displayed image through a CRT and the like is time divided and the image for the right eye and the image for the left eye are alternatively sent to right and left eyes respectively. There are mainly following two methods according to the position where the optical shutter is placed.
(1) A method to use glasses with a liquid crystal optical shutter.
For instance, the following three-dimensional television is proposed (Japanese Patent Laid-open No. Sho 61-227498). That is, in a three-dimensional television which makes it possible to stereoscopically recognize the image of a subject by alternatively opening and shutting optical shutters prepared on each left and right glass of stereoscopic glasses in synchronization with each field of the right and left image of a subject displayed on the TV screen or in synchronization with a switching period of each field thereof, a three-dimensional television is proposed which is provided with a driving means that alternatively supplies designated AC voltage to both liquid crystal cells in synchronization with switching of the image, using a twisted nematic liquid crystal cell as the optical shutters of both eyes for the left eye and the right eye.
(2) A method in which a liquid crystal shutter is disposed in front of a display device, and a viewer uses a pair of polarized glasses.
For instance, the following pseudostereoscopic display has been proposed, (Japanese Patent Publication No. Hei 05-78017). In a pseudostereoscopic display composed of a polarizer and a liquid crystal cell are placed leaving a space therebetween in front of a display screen, a drive circuit which changes over the polarizing directions of light transmitted from the display screen through the liquid crystal cell in a division of the images at predetermined time period is connected to the liquid crystal cell by impressing an AC voltage synchronized with a frame signal of the display screen, and a polarized glasses in which the polarizing directions of the right eye and the left eye for recognition of the displayed light are different from each other, the proposed pseudostereoscopic display is characterized in that a retardation of the liquid crystal cell is from 0.1 to 0.15 .mu.m, rotating angles of the optical axis by reversing the polarity of the applied voltage is from 70 degrees to 110 degrees, the median of two directional axes which is possible to adopt as an optical axis and a polarization axis of a polarizer nearly coincide with each other, and a polarizer of a polarized glasses is an elliptical polarizer having a polarizing ability same as or close to a circular polarizing ability.
In case of the former method (1), a liquid crystal optical shutter is used on the glasses. As a result, the weight of the glasses increases, and gives a feeling of fatigue when using for a long time, and electrode wire for driving the glasses gives the viewer a sense of incompatibility in wearing the glasses. When many viewers look at the same time, glasses with similar optical shutters are necessary, which increases the cost. Further, since a twisted nematic (TN) type liquid crystal cell is used as an optical shutter, the response delays, images flicker, and right and left images are doubled.
In case of the latter method (2), simple polarized glasses are sufficient for the viewer, and a ferroelectric liquid crystal is used as an optical shutter in the display device, which makes it possible to respond to a moving image display. However, the cell is made of a conventional glass substrate, so upsizing and application to a large size CRT and the like are difficult. Furthermore, it is necessary to make a cell retardation as small as from 0.1 to 0.15 .mu.m so that the liquid crystal cell is allowed to behave as a .lambda./4 plate. In accordance with the above mentioned reduction of the cell retardation, the actual cell thickness needs to be made considerably thin, which causes lowering of a production yield of the cell. In addition, in order to widen the rotation angle of the optical axis, material for a large liquid crystal whose tilt angle .theta. about 45 degrees is required. The electric field responsivity and orientation property are usually impaired to that extent, so development of a new material is sometimes required.
A first object of present invention is to prevent lowering of a display contrast caused by an elliptical polarization which is peculiar to the operation mode of the liquid crystal cell and to provide a three-dimensional display which can reduce an occurrence of double images of the right and left images.
As the method (2) in which a viewer uses polarized glasses, a pseudostereo display has been proposed, the pseudostereo display characterized in that a ferroelectric liquid crystal cell mixed with a dichroic coloring agent in front of the display screen, a displayed light transmitted through the liquid crystal is changed by connecting a driving means which impresses an AC voltage synchronized with an image frame signal to the liquid crystal, into two polarizing directions in a manner of division of the images at predetermined time period, a .lambda./4 plate is placed in front of the liquid crystal cell to change the displayed light to a circular polarization having a different direction, and in order to observe the circular polarization, each right and left polarizer of the polarized glasses has a circular polarization which is reverse in direction to each other. (Japanese Patent Publication No. Hei 6-29914).
When using this system, because the cell uses a glass substrate, it is difficult to upsize and also difficult to apply to a large size CRT. And it results in a high cost as a system due to the usage of a .lambda./4 plate and a circular polarizer.
Furthermore, another three-dimensional image display is proposed. In a three-dimensional image display which has a moving image display to display an image signal on a screen, a polarizer provided in front of the moving image display, a liquid crystal panel provided in front of the polarizer, for switching the polarizing direction based on a synchronizing signal with the aforementioned image signal, and polarized glasses in which the polarizing directions of a right and left polarizer differ from each other by 90 degrees and which transmit and shield the light of the image, the proposed three-dimensional image display is characterized in that the material of liquid crystal for a liquid crystal panel is mixed with one percent or less by weight of a multichroic coloring agent to reduce the effect of the elliptical polarization and improve the visivility. (Japanese Patent Publication No. Hei 8-23663).
Since this display uses the conventional TN cell, a moving image display at high speed is not available due to the special quality thereof. In addition, since the multichroic coloring agent which is mixed to improve visivility, further hinders responsivity, the mixing amount of the coloring agent can not be more than 1%. And another disadvantage is that the above display can not be applied to a moving image display with a large screen because it uses the conventional type liquid crystal cell.
A second object of the present invention is to provide a three-dimensional display which can be applied to a large size display device and respond to a high speed motion.